How "slo can you go" "how little can you burn"

[nels]

Hello group,

This is my first post on the forum. I haven't flown in thirty years but have decided to return to the sport or hobby or bank account drain or what ever you might call it. I've been watching the site for several months and notice performance comments are always pointed toward how fast your plane can go on how little fuel.  In my early, pre family days, I flew a Cessna 150 but even then admired and dreamed of owning a Mooney. In those days and it seems even now, it was how fast and how frugal they are to fly. Now that I'm older and retired I am looking at both sides of the flight experience; the part I think I understand which is the speed, but what about the Sunday liesurely cruise around the country side. How "slo can you go" while still retaining good control surface performance and "how little fuel can you burn" at the lower speeds. The old Cessna I remember (?) popping along at about 95 knots and using about 5 gph.  How close can a Mooney get to this laid back economical cruise? At the lower speeds does the interior noise drop off significantly?

With any luck I hope to be joining you guys and gals in the Mooney experience in the very near future.

 

[Shadrach]

I don't recall 150s being quite that thrifty. I'm guessing that 5.5gph ~peak should net ~110-115kts in a vintage 4cyl bird...

[N601RX]

The 150 we had was more like 95mph instead of 95knots on 5 gallons . 

[The-sky-captain]

I haven't played around with it much but 19 squared gives me around 6 gph at 110 knots in my J.

[1964-M20E]

When I go out just to “play” and I’m not going anywhere I’ll back off to about 20”MP, and 2400RPM generally doing about 110kts GS and leaned out will but in the neighborhood of 6 to 7 GPH.  You could back it off even farther down to 15 or 16”MP and go about 80 to 90KTS on even less fuel.  However, when you are ready to go somewhere you can crank it up and get there a lot faster than the 152 or 172.  I does get quieter but I have not paid much attention since I always have my headset on.

[Shadrach]

Quote: The-sky-captain

I haven't played around with it much but 19 squared gives me around 6 gph at 110 knots in my J.

[The-sky-captain]

I'd say I was at peak or a little over. It's been a couple years since I've experimented with it.

[nels]

Quote: N601RX

The 150 we had was more like 95mph instead of 95knots on 5 gallons . 

[MooneyMitch]

"I'm also trying to rule out any reason not to buy one."

 

If you can afford to own the plane, there is no reason not to buy one!! 

[MARZ]

When I take family and friends up to bore holes in the sky I'll usually run 21/25 

[MARZ]

Quote: Mitch

"I'm also trying to rule out any reason not to buy one."

 

If you can afford to own the plane, there is no reason not to buy one!! 

[Immelman]

In my E model if I am going to tool around and sight see, 6-6.5 gph is easily achievable, andnets around 120mph indicated airspeed. That's 2400 rpm, lean of peak.

The lowest consumption I can get while remaining aloft is down closer to 5gph, 1900rpm, airspeed near best glide. Thing is though, running around at that power setting isn't nearly as sustainable without periodically fiddling with the power. If you get a little down-draft or do some maneuvering, either more power or a descent are required lest the angle attack come up where induced drag starts taking over (back side of the power curve).

Becuase of this for 'best economy set the power and forget it' sightseeing, plan on 6gph in a vintage mooney.

If you go out and find some ridge lift you can get it down further, but at some point the engine starts getting cold...

[jlunseth]

In theory, L\D max (best glide) will give best range.  Would be interesting to throttle back to about 60% then pull it LOP as far as it will go and stay smooth, until you hit max glide.  Mine is about 85.

 

[M20F]

http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=2&threadid=1050

115 knots TAS at 5.2gph coast to coast non-stop

[nels]

Quote: M20F

http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=2&threadid=1050

115 knots TAS at 5.2gph coast to coast non-stop

[1970m20e]

[nels]

Quote: 1970m20e

[xftrplt]

Quote: jlunseth

In theory, L\D max (best glide) will give best range.

[Hank]

Best Range is the Carson speed. Going by memory, it's about 1.3 Best Glide.

So my glide speed is 105 mph; Carson speed [from previous calculations] is about 138 mph. No thank you, I don't cruise that slow, only for flightseeing.

[Hank]

You're right, there, Jim. At altitude, I often indicate in the 135-140 mph range; GS varies from 105-180 knots. Gotta love headwinds!

Now I'm going to have to dig out the Carson speed stuff and go over it again to see just where it is . . . . . . Thanks for that!

[xftrplt]

Carson Speed is not Max Range Speed.

It considers the need for speed--an economic or psychological issue--and is, therefore, faster than Max Range. 

------

Maximum Range

To maximize the range, we want to get the maximum distance for each pound of fuel burned. Starting with our basic relation

 

or, splitting out the units

 

Now if we divide both sides by velocity, we get

 

Dividing out the hours, we get

 

Note that the left side is what we wanted, pounds of fuel per nautical mile. To minimize the pounds of fuel per nautical mile, we can minimize the ratio of power over velocity. Looking at the power required chart, a line from the origin to any point on the curve has the slope of power over velocity (P/V). As you trace a line from the origin to each point on the curve, the slope will be a minimum when the line is tangent to the power required curve. Therefore, the maximum range airspeed occurs where a line from the origin is tangent to the power required curve. This also corresponds to the minimum point on the thrust required curve (drag polar).

[201er]

Some posts here don't make sense to me like doing 20" and 2400RPM. If you wanna go slow and reduce you fuel burn, it makes sense to bring that prop back. On the other hand some folks suggested really low MP or 19 squared but that puts you in the yellow caution range on the tach (unless it's just for 201s). The lowest manageable power setting I find to be 20"/2000RPM and back to 20LOP. This brings it down to 6gph and 110knots. Still faster than a skyhawk and lower fuel burn (I remember 105knots at 8.5gph in 172). I don't see any point of cruising slower than this.

[jetdriven]

What we have found is the NMPG improvement from 65% power to, say, 50% power is only around 1.5 to 2 NMPG better.  But the variable airframe costs are fixed, so you offset much of that with higher airframe expenses. In the end, it is only a couple gallons more fuel to save some time, so 65% ends up being where we cruise all the time, except above 7K where you can't get it.

[nels]

When I hear someone say, for instance, that an E model cruises at 150 knots, should I presume that is 100% power? So at 65% power what is the cruise and consumption with, say an E model, or in the above cases, your 201's.

[jetdriven]

I can tell you from experience that everything forward at sea level, in an early 201, is 18-18.5 GPH and 168 KTAS. Pulling it back to 10 GPH (75% power) nets you 150-155 KTAS.